PKOGRESS IN BIOLOGICAL INQUUtlES, 19 3 2 129 



the rnto of 11,579 fingcrlings por acre or a survival of 46.2 percent. 

 The results indicate, as anticii)ate(l, that the blackhead and blunt- 

 nosed minnows are eciually valuable as fora(2;c fish. 



Crapple and hlueglil suniitih. — It has been found that crappie and 

 bluegill sunfish make a very satisfactory combination, the production 

 of crappie lingerlinj2;s being somewhat greater than when the pond is 

 stocked with crappie alone. The young bluegills are evidently j^reyed 

 upon by the crappie since only a comparatively small number of 

 fingerlings of this species are produced under such conditions. This 

 being the case it appeared that the production of bluegills might be 

 increased by the use of minnows. Accordingly a pond was stocked 

 with adult black crappie and bluegills as usual and in addition 12,000 

 blackhead minnows were placed in the pond to serve as forage. The 

 yield from the pond was 19,164 crappie and 22,680 bluegills per acre, 

 with a combined weight of 115 pounds. In 1931 the same combina- 

 tion without the blackhead minnows gave 20,562 crappie and 1,430 

 bluegills per acre. It is evident that the addition of forage minnows 

 increased the yield of bluegill sunfish without materially affecting the 

 number of crappie. 



Effect of high-oxygen concentrations. — Dr. Wiebe has continued his 

 experiments on the effects of high concentrations of dissolved oxygen, 

 using brook and rainbow trout of various sizes. The results of these 

 experiments are in full accord with those previously obtained with 

 bass and other pond fish. 



It was found that trout can withstand rapid changes from low to 

 high concentrations of oxygen without injury. In some instances the 

 fish were exposed to oxygen at from 10 to 20 pounds pressure for 46 

 hours without suffering any injurious effects. Even when suddenly 

 transferred from water containing 51.8 parts per million of oxygen to 

 water w^ith an oxygen content of only 8.4 parts per million the fish 

 showed only momentary signs of distress and no after effects were 

 evident. 



In another experiment brook and rainbow trout fingerlings were 

 kept for 20 days in open tanks containing water supersaturated with 

 oxygen. During this period the concentration of oxygen ranged from 

 21 to 33 parts per million and at no time was the saturation below 

 200 percent. The fish all survived the experiment and there was no 

 evidence that they were affected adversely by the high-oxygen con- 

 centration. No case of gas bubbles or popeye was observed although 

 the fish were watched carefully for these symptoms. 



Experiments on the ability of fish to use oxygen at different hydro- 

 gen-ion concentrations show that largemouth and smallmouth black 

 bass, green sunfish, crappie, yellow perch, and rainbow trout have 

 the ability to extract oxygen from the water at low-oxygen tensions 

 equally well over a wide range of hydrogen-ion concentrations. The 

 bluegill sunfish has a somewhat narrower range of toleration while 

 in the steel colored and blunt-nosed minnows the range is much more 

 limited. Outside of the normal pH range of the species in question 

 the lethal-oxygen tension is dependent in large measure on the initial 

 amount of oxygen in solution. 



Rate of digestion in bass. — A series of experiments by H. C. Markus 

 to determine the rate of digestion in largemouth black bass at various 

 temperatures gave some very interesting results. It was found that 



